As a crystal structure of carbon, diamond and graphite have been known from long time ago, and (C60) was found by R. E. Smalley, R. F. Curl and H. W. Kroto et al., in 1985 (Nature, 318: 162-163, 1985). C60 has a soccer ball-like structure comprising 12 pentagons and 20 hexagons, and other than C60, there are large basket-like molecules such as C70 and C76, and this series of molecules is called “fullerene”. Further, carbon compounds with new structures previously unknown, such as “carbon nanotube” (Nature, 354: 56-58, 1991; Japanese Laid-Open Patent Application No. 2001-64004) and “carbon nanohorn” (Chem. Phys. Lett., 309, 165-170, 1999; Japanese Laid-Open Patent Application No. 2001-64004) were successively discovered by one of the present inventors, Sumio Iijima, in 1991 and 1999, respectively. All of these fullerenes, carbon nanotubes and carbon nanohorns comprise six- and five-membered rings of carbon atoms, and form nanometer-scale fine structures, and therefore, they have got a lot of attention as “nanographite structure” recently.
The reasons why nanographite structures get a lot of attention include: “carbon nanotubes can have both properties of metal and semiconductor due to the difference in their chirality (Nature, 391: 59-62, 1998)”, “metal-doped fullerene exhibits superconductivity (Nature, 350: 600-601, 1991)”, “selective gas storage capability shown by carbon nanohorns (Nikkei Science, August issue, 42, 2002)”. With the use of these characteristic properties, nanographite structures are expected to be applied to new electrical materials, catalysts, optical materials, and other such fields, more specifically, to wiring of semiconductors, fluorescent indicator tubes, fuel cells, gas storage, carriers for gene therapy, cosmetics, drug delivery systems, biosensors, etc.
As mentioned above, when application of nanographite structures is considered in various fields, techniques for efficient recognition, binding, separation, alignment of carbon nanotubes, carbon nanohorns or modified materials thereof, are required. However, there is a problem that it is hard to use nanographite structures such as carbon nanohorns and carbon nanotubes because, in general, there is no method for recognizing, binding them specifically. The object of the present invention is to provide: a peptide or a phage recognizing nanographite structures which allows efficient recognition, binding, separation, alignment of nanographite structures such as carbon nanohorns and carbon nanotubes; an artificial protein or a chimeric molecule comprising the peptide bound to a functional peptide or protein, or a labeled material, etc.; a complex formed from the peptide molecule, the artificial protein or the chimeric molecule, and a nanographite structure.
The present inventors have conducted keen study to attain the above-mentioned object, and have found that peptides capable of binding to nanographite structures, which specifically recognize nanographite structures such as carbon nanohorns and carbon nanotubes, etc., can be obtained by a process comprising steps of: treating a nanographite structure with nitric acid to construct a carboxyl group on the nanographite structure; biotinylating the carboxyl group; solid-phasing the biotinylated nanographite structure on a magnetic bead coated with streptavidin; repeating a panning operation to concentrate a phage clone binding to a nanographite structure, wherein said panning operation comprises following steps: a phage population wherein various peptide sequences are displayed on phage particles is brought into contact with the solid-phased nanographite structure; the solid-phased nanographite structure to which phage particles have bound through the peptide sequences is collected with a permanent magnet; phage particles bound to the obtained nanographite structure are proliferated in E. coli; then a proliferated phage population wherein peptide sequences are displayed on phage particles is brought into contact with the solid-phased nanographite structure again. Thus the present invention has been completed.